1. Field of the Invention
This invention relates to a process for producing a superconducting compound tape or wire by irradiation of electron beams.
2. Description of the Prior Art
A superconducting material having an electric resistance of zero can permit flowing of a large current without power consumption, and the superconducting state is maintained even in a high magnetic field. Because of this characteristic, superconductor materials have come into increasing use as coil materials for electromagnets generating a high magnetic field which are used, for example, in an NMR CT scanner, an energy storage device, a nuclear reactor, and a particle accelerator for high-energy physics.
Alloys such as Nb-Ti and Nb.sub.3 Sn and V.sub.3 Ga, called A-15 type compounds, have previously been used as superconducting materials used in coil materials of electromagnets capable of generating a high magnetic field.
The Nb-Ti alloy has high plasticity and can be directly worked into a wire or tape. Nb.sub.3 Sn and V.sub.3 Ga, the A-15 type compounds, are hard and brittle and cannot be directly worked. Hence, working of these A-15 type compounds into a wire or tape relies on a diffusion reaction by a surface diffusion method or a so-called bronze method.
The upper critical magnetic fields H.sub.c2 of Nb-Ti, Nb.sub.3 Sn and V.sub.3 Ga at 4.2 K are 12 T, 21 T and 22 T (T=tesla), respectively. As the applied magnetic field approaches the upper critical magnetic field, the critical current density rapidly decreases. Accordingly, even when a V.sub.3 Ga wire is used, the magnetic field generated by a superconducting magnet is 17.5 T at the highest. On the other hand, as the utility of superconductors has been developed, the superconducting magnets have been required to generate a stronger magnetic field, and it has been desired to develop superconducting wires or tapes having higher performance. For example, it is said that a superconducting magnet for Mirrer-type fusion reactors is required to generate a magnetic field of 20 to 24 T. Such a high magnetic field is difficult to obtain by existing Nb.sub.3 Sn and V.sub.3 Ga.
On the other hand, Nb.sub.3 Al, Nb.sub.3 (Al,Ge) and Nb.sub.3 Ga, which are the A-15 type compound, PbMo.sub.6 S.sub.8, which is a Chevrel type compound, and NbCN, which is a B1-type compound, have been discovered as compounds having excellent superconducting properties.
The H.sub.c2 values of Nb.sub.3 Al, Nb.sub.3 (Al,Ge), and PbMo.sub.6 S.sub.8 are 30 T, 41 T and 50 T, respectively, which are higher than those of Nb.sub.3 Sn and V.sub.3 Ga. If, however, such materials are to be produced by the conventional diffusion method, the heat-treating temperature must be very high. Consequently, the crystal grains become large, and the critical current density Jc of the resulting materials, which is of importance in practical applications, is markedly reduced.